Regulating overtravel in bi-furcated plugs for use in valve assemblies

ABSTRACT

A gap control device that works with a plug on a valve assembly for use in high-temperature applications. The plug may include two parts and a compressible seal that, when compressed, engages with an adjacent wall of a cylinder or “cage” typical of a trim assembly. In one embodiment, the gap control device forms a hard stop that expands in response to high temperatures. This feature prevents excess over-travel between the two parts of the plug in the high-temperature applications so as to limit stress and wear on the compressible seal.

BACKGROUND

Flow controls are important in many industries. Valve assemblies are atype of flow control that are ubiquitous on process lines, gasdistribution networks, or any system that carries flowing material.These devices regulate material flow within set parameters, or, in caseof problems, shut-off flow altogether. To do this, the devices oftenleverage mechanical mechanisms to regulate flow for this purpose. Themechanisms may include an actuator that couples with a valve, typicallyhaving a closure member and a seat. The closure member may embody aplug, a ball, a butterfly valve, or like implement that the actuatormoves to positions relative to the seat. These positions define flow ofmaterial through the device, including, for example, open positions thatallow flow through the device and a closed position, where the closuremember contacts the seat to prohibit flow.

SUMMARY

The subject matter disclosed herein relates to improvements toaccommodate applications that expose valves (in valve assemblies) tomaterial at extreme temperatures. Of particular interest herein areembodiments that regulate movement of parts found in a bi-furcated plug.This type of plug is often found in valve assemblies that can handlematerial at very low temperatures (e.g., at or less than −150° F.) orvery high temperatures (e.g., at or greater than 600° F.). The plug mayhave two parts and a resilient seal that separates the parts under load.Relative movement between the parts can compress the resilient seal sothat, in most cases, the resilient seal contacts another part of thevalve assembly. The embodiments are useful to ensure that movementbetween the parts is repeatable and predictable. For high temperatureapplications, this feature can avoid unnecessary wear and limit stresseson the resilient seal that may result from over-travel due to expansion(or like thermal changes) of the parts that occurs in response to thematerial temperature.

DRAWINGS

Reference is now made briefly to the accompanying drawings, in which:

FIG. 1 depicts a schematic diagram of an exemplary embodiment of a gapcontrol device as part of a valve.

FIG. 2 depicts a schematic diagram of the gap control device of FIG. 1in a first thermal configuration;

FIG. 3 depicts a schematic diagram of the gap control device of FIG. 1in a second thermal configuration;

FIG. 4 depicts a schematic diagram of the gap control device of FIGS. 2and 3 as part of a trim assembly;

FIG. 5 depicts an elevation view of the cross-section from the side ofan example of the trim assembly of FIG. 4; and

FIG. 6 depicts an elevation view of the cross-section from the side ofthe gap control device of FIGS. 2 and 3 as part of an example of a valveassembly.

Where applicable, like reference characters designate identical orcorresponding components and units throughout the several views, whichare not to scale unless otherwise indicated. The embodiments disclosedherein may include elements that appear in one or more of the severalviews or in combinations of the several views. Moreover, methods areexemplary only and may be modified by, for example, reordering, adding,removing, and/or altering the individual stages.

DETAILED DESCRIPTION

The discussion that follows describes embodiments of a gap controldevice that can operate to regulate over-travel in bi-furcated plugs.However, the concepts may apply to other closure members or, generally,to valves (and valve assemblies) that need to control relative movementor position between two or more components. It is not uncommon, forexample, that operating conditions can induce changes (e.g., thermalexpansion or contraction) in these components. Efforts to manage thesechanges through design and manufacture can address some of the potentialissues that arise at the device in the field. But some applications mayneed to meet certain standards or specifications that can test limits offits, tolerances, and like engineering practices. The embodiments hereinmay supplement these practices to improve performance or, at least,extend life of parts to avoid costly maintenance and repairs. Otherembodiments may be within the scope of this disclosure as well.

FIG. 1 depicts a schematic diagram of an exemplary embodiment of a gapcontrol device 100 that can address some of these potential issues. Thegap control device 100 is shown as part of a valve 102 that regulatesflow of material 104 in a valve assembly, identified generally bynumeral 106. Examples of material 104 may include fluids, solids, andfluid/solid mixes, as well. The valve 102 may have a pair of valvecomponents (e.g., a closure member 108 and a seat 110). The closuremember 108 may comprise a plug 112 having a bifurcated structure withtwo parts (e.g., a first part 114 and a second part 116). The structuremay also incorporate a seal 118 that operates to form a gap 120 betweenthe parts 114, 116. The gap control device 100 may form a hard stop 122that interacts with the parts 114, 116. In operation, the valve assembly106 applies a load L to the closure member 108 so the plug 112 contactsthe seat 110 and arranges the valve 102 in a closed position. The load Lmay cause the second part 116 to “over-travel” relative to the firstpart 114. This over-travel reduces the gap 120 enough to deform the seal118. For high-temperature applications, this feature is useful to meetoperative standards for Class V or “effectively zero-leakage” devices.

Broadly, the gap control device 100 can be configured so that the hardstop 122 actively controls relative travel between the parts 114, 116.These configurations may limit stress and wear in the seal 118 that mayarise because of changes in the parts 114, 116 or other parts of thevalve assembly 102. Thermal expansion due to high-temperature materials(e.g., material 104), for example, may allow the second part 116 to movemore without any increase to load L. In turn, the gap 120 assumes adimension in the closed position that is smaller than its “nominal”dimension that is typical of operation of the valve 102 with material104 at room temperature. Use of the gap control device 100 maintains thedimension of the gap 120 at or near this nominal dimension independentof temperature of the material 104. This feature avoids unnecessarystress and wear on the seal 118 because the hard stop 122 ensuresrepeatable, predictable over-travel of the second part 116 relative tothe first part 114 at both nominal or “room” temperature and at elevatedtemperatures that occur in high-temperature applications. As an addedbenefit, “active” control of the gap 120 could reduce costs ofconstruction because the plug 112 could employ different, less costlymaterials yet still meet stringent operation requirements for hightemperature applications, particularly in high-temperature applications(where the operating temperature may exceed 600° C. or more).

The valve 102 may find use in myriad of applications. These devices canincorporate into systems for use in oil and gas processing, powergeneration, refining, chemical and petrochemical, and water control.These industries often deal in processes that transmit materials underhigh-temperature and pressure. Such parameters may limit or constraindesigns for the valve 102 and its components.

The two-part plug 112 is useful to meet some of these design challenges.Advantageously, its construction can “actuate” the seal 118 to meet morestringent operating requirements without sacrifice to operating speed orresponsiveness. This construction may use materials with propertiesparticularly suited to material 104, or more generally that comport withpressure, temperature, chemical characteristics, cost, and systemconstruction. Exemplary materials include titanium, duplex stainlesssteels, and Nickel alloys, to name only a few.

The seal 118 may be configured to change shape in response to movementof parts 114, 116. Resilient materials like spring steels may proveuseful so that the seal 118 can accommodate different dimensions of thegap 120. When compressed, the resilient device may extend from theperiphery of the plug 112, for example, to contact proximate structures,like a cage discussed more below.

FIG. 2 depicts a schematic diagram of an example of the gap controldevice 100 of FIG. 1 to inform the discussion of its design. The hardstop 122 may include a thermally-active member 124 with a thermal core126 that forms a stopping surface 128 proximate the gap 120. The thermalcore 126 may embody an elongate cylinder, although other geometries,like cubes or spheres, may suffice as well. The elongate cylinder may bedisposed in the first part 114 or the second part 116, as desired.Suitable materials for the thermal core 126 may have homogenous ornon-homogenous compositions. Care may be taken to ensure the materialhas a coefficient of expansion (“COE”) that will cause the thermal core126 to respond to the operating temperature independent of (or at adifferent rate than) the parts 114, 116. In one implementation, theelongate cylinder may assume a thermal configuration that correspondswith its thermal response to temperature of material 104. At nominal orroom temperature, the thermal configuration sets a first position forthe stopping surface 128 that does not interfere with over-travel of thefirst part 114. The stopping surface 128 may reside outside of gap 120;for example, co-planar with the top surface of the first part 114 or,even, below the top surface altogether.

FIG. 3 shows the example of gap control device 100 of FIG. 1 toillustrate another thermal configuration for the elongate cylinder. Thisthermal configuration may correspond with thermal expansion of theelongate cylinder. As shown, the elongate cylinder may embed into thefirst part 114 to expose only the top, stopping surface 122. Thisfeature may operate to constrain expansion in all directions but one,identified by the arrow E. The thermal expansion can set a secondposition for the stopping surface 128 that is different from the firstposition (e.g., in FIG. 2). Preferably, the stopping surface 128 is“above” the first part 114 or closer to the second part 116, as measuredby a dimension D between the stopping surface 126 and the top surface ofthe first part 114. Values for the dimension D may be calculated basedon thermal properties and geometry for the thermal core 126. It may bebeneficial that dimension D is set at least to avoid total collapse ortotal compression of the seal 118.

FIG. 4 depicts a schematic diagram that shows an example of the gapcontrol device 100 of FIG. 2 with additional details of the valvecomponents. The valve assembly 106 may include an actuator 130 thatcouples with the plug 112 via a stem 132. The valve assembly 106 mayalso include a trim assembly 134 having a cylinder 136 (also “cage136”), with a peripheral wall 140 that circumscribes an axis 142 to formbore 144. The peripheral wall 140 may have one or more openings (e.g., afirst opening 146 and a second opening 148). The openings 146, 148 theopenings 146, 148 may be perpendicular to the axis 142 and penetrate theperipheral wall 140 to allow access to the interior of the bore 144. Inone implementation, the plug 112 may include a piston seal ring 150,shown here as an annular ring, typically graphite or metal, thatcircumscribes the outer surface of the first part 114. When in use, thisannular ring may remain in contact with the bore 144, which helps toreduce pressure drop and velocity as the plug 112 moves away from theseat 114. The piston seal ring 150 can also help damp vibrations in thestem 132. As also shown, the seal 118 may embody a resilient element 152(like a constant-force spring) that resides between the parts 112, 114of the plug 112. Examples of the resilient element 152 may includespring washers, like Belleville washers, that deform under substantiallyuniform loading (e.g., constant load L).

Some implementations of the valve assembly 106 may be configured to“balance” pressure of material 104 across the plug 112. This feature mayrequire openings O in the plug 112. The openings O operate to allowupstream or downstream pressure to act on both sides of the plug 112.The actuator 130 is often smaller in these designs because the higher,upstream pressure that are responsible for “unbalanced” forces do notact on the plug 112.

The trim assembly 134 may be configured for the valve assembly 106 tooperate in applications that require any one of the standard leakclassifications for control valves. These configurations may, forexample, operate to “effectively zero leakage” or IEC 60534-4 Class Vstandards. This feature maintains maximum leakage through the valve at0.0005 ml of water per minute, per inch of port diameter per PSIdifferential pressure, typically measured from valve inlet to valveoutlet with leakage contributed by the interface between the plug 112and seat 114, gaskets between components of the trim assembly 134, andbetween the “balance” seal and the cage 138 or plug 112. In theover-travel position, the bifurcated plug 112 compresses the spring 152,which urges the resilient element 152 into contact with the bore 144 toprovide tight shutoff.

FIG. 5 depicts an elevation view of the cross-section from the side ofan example that shows additional structure for use with the gap controldevice 100. The first part 114 may have an annular body 154 with acentral axis 156. A groove 158 may penetrate the outer surface toreceive the piston seal ring 150. On its bottom, the annular body 154may have a central aperture 160 that aligns with the central axis 156.The central aperture 160 may terminate at a bottom surface 162. On thetop, the annular body 154 may have a recess 164 that forms a surface166. The recess 164 may have an offset bore 168 that is offset from thecentral axis 156 towards the periphery of the annular body 154. The core126 may reside in the offset bore 168. As also shown, the second part116 may form an annular disc 170 with a central axis 172. On one side,the annular disc 168 may have an annular boss 174 that terminates at aperipheral step 176 that forms a step surface 178. The opposite side ofthe annular disc 170 may include a protruding boss 180. A central bore182 may penetrate through the body 154 and disc 170 along the axes 156,172. When assembled, the annular boss 172 fits into the recess 162. Thespring 152 resides between the top of the annular body 154 and the stepsurface 178 of the annular disc 170. The stem 132 may extend through thecentral bore 182. As shown, the trim assembly 110 may include a coilspring 184 that inserts over an exposed end of the stem 132 to reside inthe central aperture 160. A retaining ring 186 (like a washer) mayreside on the stem 132 to maintain the coil spring 184 in its positionagainst the bottom surface 162. Complimentary threads on the stem 132and second part 116 may secure the stem 132 to the plug 112 and, thus,secure the part in position with appropriate pre-load or compression ofthe coils spring 184.

FIG. 6 depicts an elevation view of the cross-section from the side ofan example that shows additional structure for use with the gap controldevice 100. Structure for the valve assembly 106 may include a valvebody 188 that couples with a bonnet 190 via one or more fasteners F. Thevalve body 188 may also have a flowpath 192 that terminates at open ends(e.g., a first open end 194 and a second open end 196). Flanges 198 orbutt-weld ends at the open ends 194, 196 may be configured to couplewith sections of pipes or pipelines. In use, this structure may enjoyuse across a wide spectrum of applications. Also known as a “controlvalve,” the device may integrate into process control systems (or“distributed control system” or “DCS”) with a control loop. Thesesystems may manage operation of many different flow controls, includingthe valve assembly 106. The control loop, for example, may generatesignals (or “control signals”) that cause the valve assembly 106 toactivate the actuator 130 to position the plug 112 relative to the seat110.

In light of the foregoing discussion, embodiments of the gap controldevice 100 proposed herein can maintain repeatable, reliable movement ofthe parts in bifurcated plugs. These improvements can extend lifetime ofresilient seals that separate the parts and outfit these plugs for usein high-temperature applications.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. An element or functionrecited in the singular and proceeded with the word “a” or “an” shouldbe understood as not excluding plural said elements or functions, unlesssuch exclusion is explicitly recited. References to “one embodiment” ofthe claimed invention should not be interpreted as excluding theexistence of additional embodiments that also incorporate the recitedfeatures. Furthermore, the claims are but some examples that define thepatentable scope of the invention. This scope may include andcontemplate other examples that occur to those skilled in the art. Suchother examples are intended to be within the scope of the claims if theyhave structural elements that do not differ from the literal language ofthe claims, or if they include equivalent structural elements withinsubstantial differences from the literal language of the claims.

Examples appear below that include certain elements or clauses one ormore of which may be combined with other elements and clauses describeembodiments contemplated within the scope and spirit of this disclosure.

What is claimed is:
 1. A valve assembly, comprising: an actuator; avalve coupled with the actuator, the valve comprising a closure memberand a seat, the closure member comprising two pieces that are moveablerelative to one another under load from the actuator; and a gap controldevice disposed in proximity to the two pieces of the closure member,the gap control device comprising a hard stop that prevents relativemovement between the two pieces.
 2. The valve assembly of claim 1,wherein the hard stop resides between the two pieces of the closuremember.
 3. The valve assembly of claim 1, wherein the hard stop isdisposed in one of the two pieces of the closure member.
 4. The valveassembly of claim 1, wherein the hard stop comprises material thatexpands under temperature at a rate that is different from material ofat least one of the two pieces of the closure member.
 5. The valveassembly of claim 1, wherein the hard stop forms a stopping surfacehaving a first position and a second position, each corresponding withthermal properties of the hard stop at different temperatures.
 6. Thevalve assembly of claim 1, wherein the hard stop comprises athermally-active member disposed in one of the two pieces of the closuremember and comprised of material that expands and contracts in responseto different temperatures.
 7. The valve assembly of claim 1, wherein thehard stop forms a core that extends into one of the two pieces of theclosure member.
 8. The valve assembly of claim 1, further comprising: acompressible seal disposed between the two pieces of the closure member.9. The valve assembly of claim 1, further comprising: an annular ringcomprising resilient material disposed between the two pieces of theclosure member.
 10. The valve assembly of claim 1, further comprising: acylinder having a peripheral wall circumscribing the two pieces of theclosure member.
 11. A valve assembly, comprising: a valve body forming aflow path for material; a trim assembly disposed in the valve body, thetrim assembly having a cylinder and a plug disposed inside of thecylinder, the plug having a first part, a second part, and a resilientseal member disposed therebetween so as to form a gap between the firstpart and the second part, the plug further comprising a gap controldevice that prevents relative movement between the first part and thesecond part.
 12. The valve assembly of claim 11, wherein the gap controldevice forms a cylindrical plug in one of the first part or the secondpart that comprises material with a coefficient of thermal expansionthat is different from the coefficient of thermal expansion of the firstpart and the second part.
 13. The valve assembly of claim 11, whereinthe gap control device comprises material that expands at a rate that isdifferent from either the first part or the second part.
 14. The valveassembly of claim 11, wherein the gap control device comprises athermally-active member having an end that changes position relative tothe first part and the second part in response to temperaturedifferential of material in the flow path of the valve body.
 15. Thevalve assembly of claim 11, further comprising: a valve stem extendingthrough the first part and the second part; and a coil spring disposedon an end of the valve stem.
 16. A method, comprising: operating a valveassembly to regulate flow of material by, moving a first part of atwo-part plug to a closed position against a seat; overdriving a secondpart relative to the first part in the closed position to compress aseal ring; and stopping compression of the seal ring with a hardstophaving a stopping surface that prevents travel of the second part,wherein the stopping surface varies in position in response totemperature of the hardstop.
 17. The method of claim 16, wherein thestopping surface is set in from peripheral edges of the first part andthe second part.
 18. The method of claim 16, wherein the hardstopcomprises material that expands at a rate that is different from eitherthe first part or the second part of the two-part plug.
 19. The methodof claim 16, wherein the stopping surface resides in between the firstpart and the second part.
 20. The method of claim 16, wherein thehardstop is disposed in the first part.